The present invention relates to controllable and improved air assists for insuring uniform conveying of particulate material in a dense phase bulk material handling system.
Pneumatic transportation of materials has been shown to be an efficient way of transporting bulk particulate materials within plants using such materials. The transporting of these particular, that is granular or powdered material is generally done in two types of pneumatic conveying. The first is a "dilute" phase pneumatic conveying system that utilizes low air pressure, generally 15 psi and below with a high air volume relative to the volume of the material being conveyed. A fan or a low pressure blower is used for introducing air into the conveying line. A "dense" phase bulk material transport system has a much higher ratio of material to air and utilizes higher pressure air, generally from about 15 to 70 psi and above. Pressure ranges are commonly up into the 50-60 psi range in dense phase transporters of the type shown herein.
U.S. Pat. No. 4,955,761 to Fedderhorn et al. illustrates a dense phase pneumatic conveying system which introduces a gas under pressure into the transporting conduit in a direction that is generally transversely in the direction of conveying movement, but the system relies on forming plugs in the conduit which are separated from each other by cushions of air. This patent relates to removing plugs at bends of conduits, while the present invention is directed toward maintaining a relatively uniform flow to avoid plugs or slugs from causing high energy impact at bends of conveying conduits.
U.S. Pat. No. 3,295,896 illustrates a pneumatic transportation system for bulk material that is pulverant, powdery, granular or fragmented. This involves a series of compartmented sections in a transporter system, and not a continuous flow system. The batches of material are conveyed by compressed air, and the pressures that are used for conveying in each compartment are successively lower from the source to the receiving bin. Fluidizing cells are used in each compartment to feed the conveying air into the compartment in a lateral direction. Pressure transducers are utilized for determining the regulated pressure in the next subsequent compartment on the conveying conduit. The pressure transducers are used for controlling the valves at the inlet to each compartment as well.
U.S. Pat. No. 2,739,845 shows a granular material conveyor which utilizes a tapered conduit, but utilizes air injection manifolds to inject air in response to differential pressure controllers. Pressure gradients within the conduit or line are used for control, and if the pressure decreases additional quantities of supplemental conveyance fluid are injected.
U.S. Pat. Nos. 4,861,200, and 4,909,676 show the ability to add air to aid in dislodging clogged areas, but these devices operate on differential pressure switches.
U.S. Pat. No. 4,955,761 is a dense flow conveying device, and a valve is operated to inject air into the conduit when pressure increases in a section of the conduit.
U.S. Pat. No. 4,715,748 is a bulk conveying system that also uses air inlet valves that are pressure sensitive to blockages downstream so that if air pressure rises upstream of a blockage it actuates a diaphragm that opens the valve and permits air under pressure to be provided.
A pneumatic conveyor tube booster valve is shown in U.S. Pat. No. 3,708,207.
None of the patents show the provision of zoned air assists that are pressure regulated in decreasing pressure in a continuous conveying line from the source to the receiver utilizing plant line pressure for the air inputs.